The signal/noise ratio is an in-house parameter developed to help evaluate the quality of the measured autocorrelation function (ACF). It reports on the quality of the ACF from a single acquisition, but not on the quality of the sample being measured.

Considering the fact that the ACF is by definition a series of exponential decays determined by the size and diffusion coefficient of the particles in solution, any deviation of the ACF from the curvature described by an exponential decay is due to experimental noise and not caused by the Brownian motion of particles in solution. Determination of the signal/noise ratio is based on a proprietary algorithm that utilizes information that includes the amplitude of the ACF and any deviation of the measured ACF from an idealized ACF (comprised purely of a series of exponential decays) at each tau.

Therefore, the signal/noise ratio is a better indicator for ACF quality than the ACF amplitude alone. Good acquisitions show signal/noise ratio values of 125 or higher. In PR.Panta Control, the signal/noise ratio is used in the automatic quality checks to decide if an ACF is valid or not.

In most cases, low signal/noise values are either caused by low sample concentration or by insufficient fluorescence which may lead to incorrect positioning of the DLS optics above the capillary. Incorrect positioning of the optics may further lead to increased scattering intensities due to flare from the capillary wall.